cure for vertical dispersion

[mgraham112]

I have put between 100 and 200 rounds through my ssk upper as of today, but I am having some real issues with vertical dispersion. I am using 220SMK on top of 11.0g of W296 and rem 91/2 srbr primer. Grouping is wonderful when the velocities fall into the same bucket, but with a 5 shot string, they can range +-70fps which is causing me a vertical group that ranges 6".. I need to try a different powder and I hope that this will cure me, but I was wondering if what other people were experiencing in fps and deviation/spread with their particular load. My next powder is N110 which from what i have read is ideal. I dont know if I should try different bullets or not. I am up for any suggestions.

[Rikky Lee]

I had exactly the same problem with the 30BR and heavy bullets - check out the threads in the other list on non-Whisper cases.

The cure is going to a faster powder. For me this was an expensive and time consuming venture but I did borrow small powder lots from shooting buddies to try.

[Alleycat]

Is 11grs subsonic? My gun would be crackin. If you are transonic you would be having issues. Do you have a chronograph? If you don't, try 9.2grs of VV N110.

[Romeyo]

Which barrel lengh does it have? I heard that barrel friction plays a serious roll when shooting jacketed bullets at subsonic velocities. I would keep the barrel as short as possible/necessary.

[Rikky Lee]

Barrel length does have an effect on velocities and juggling the powder charge to get the magic 1050fps correct.

But vertical dispersion and velocity variation is a classic indicator of the powder being too slow for the charge/case.

[mgraham112]

the barrel is a 16.5 from SSK. The velocities with 11.0 have ranged from 1250 (highest) to 1004 (lowest) with varying temps. What's weird is that the 1250 came on a day which the temp was 35 and the 1004 came on a day that was 65. very odd..... The barrel only has 100 to 200 rounds through it, so i am wondering if the velocity will settle down with a few more rounds through it....

[Rikky Lee]

No the barrel will not settle down. The velocity spikes are normal with the temperature changes if you are using the wrong powder (see http://www.sengpielaudio.com/calculator-speedsound.htm to see how the air temp affects the speed of sound). You might like to build a little table of air temp versus speed of sound.

Environmental issues also affect perceived noise but that is a separate issue.

How to deal with this - powder choice is the first challenge. Have you tried a faster powder yet?

[mgraham112]

nah, this is the only powder i have tried. I have to place an order this week for more powder and I'll get some faster ones and see how they work. Any recommendations so i dont waste any money? I have never tied any AA powder in any of my guns so I am not familiar with them. suggestions would be greatly appreciated

[Spook]

VVN 110 works nicely

[Rikky Lee]

What Spook says.

Also try to borrow faster powders from shooting buddies as you only need a small amount and everyone loves shooting a Whisper in return.